1. Field of the Invention
The present invention relates to an image processing method, image processing apparatus, and an image pickup apparatus using thereof, and particularly to an image processing method, an image processing apparatus, and an image pickup apparatus using thereof for adjusting white balance based on image data obtained by an image pickup apparatus.
2. Description of Related Art
In a digital camera apparatus such as a CCD camera, normally white balance is adjusted according to a color temperature of light source. Thus even with a change in light source type, an image shot can be displayed with appropriate colors. Specifically, an image processing apparatus mounted to an image pickup apparatus sets different gains to R, G, and B depending on light source (for example daylight, cloudy, fluorescent, incandescent, and tungsten). This enables to represent appropriate white color in any light.
In such an adjustment of white balance, integrated values of R, G, and B are calculated for each divided region and the white balance is controlled according to R/G and B/G (as disclosed in Japanese Unexamined Patent Application Publication No. 2004-173010 and Japanese Unexamined Patent Application Publication No. 2002-290987).
An image processing apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2004-173010 is described hereinafter in detail. The image processing apparatus firstly divides an input image into regions of m×n. Then R, G, and B are integrated to each of the region divided into m×n so as to calculate R/G and B/G. After that R/G and B/G calculated for each region divided into m×n is evaluated which light source type range they fall in on a light source estimated map as with the one shown in FIG. 4.
Then an Exposure Value (hereinafter referred to as an EV) at a time of shooting is read out. After that an evaluation value is calculated based on a membership function that defines a trend value with the EV read out as a variable. The evaluation value is calculated for each light source type. In case the evaluation value is more than or equal to a specified value, the white balance is adjusted with the light source type having a maximum evaluation value. However in this image processing, an evaluation of light source could be incorrect in case there is a subject with saturated brightness in a part of the divided region. That is, for a region having a brightness larger than maximum gradient, R/G and B/G cannot correctly be calculated. Thus, light source cannot be accurately evaluated.
An image processing apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2002-290987 includes a dedicated circuit for detecting saturated brightness. Thus, white balance can be more stably controlled. It has now been discovered that with this image processing apparatus, a size of the circuit increases due to the dedicated circuit. The size of the circuit is desirably small especially for a LSI for mobile devices in terms of power saving. Accordingly it is preferable to prevent mounting unnecessary circuit as much as possible. It has now been discovered that in a conventional image processing apparatus, it is difficult to adjust white balance appropriately without increasing the circuit size. The present invention is developed in light of the abovementioned problem. The present invention is purposed to provide an image processing method, an image processing apparatus, and an image pickup apparatus for easily and appropriately adjusting white balance.